Bulk-solidifying amorphous metal alloys (a.k.a. bulk metallic glasses) are those alloys that can form an amorphous structure upon solidifying from the melt at a cooling rate of several hundred degrees Kelvin per second or lower. Most of the prior amorphous metal alloys based on iron are characterized by their soft-magnetic behavior, high magnetic permeability at high frequencies, and low saturated magnetostriction [1] [2]. The Curie temperatures are typically in the range of about 200-300° C. These alloys also exhibit specific strengths and Vickers hardness two to three times those of high-strength steel alloys; and in some cases, good corrosion-resistant properties have been reported. Ferrous-based metallic glasses have been mainly used for transformer, recording head, and sensor applications, although some hard magnetic applications have also been reported.
The bulk-solidifying ferrous-based amorphous alloys are multicomponent systems that contain 50-70 atomic percent iron as the major component. The remaining composition combines suitable mixtures of metalloids (Group b elements) and other elements selected from cobalt, nickel, chromium, and refractory as well as lanthanide (Ln) metals [2] [3]. These bulk-solidifying amorphous alloys can be obtained in the form of cylinder-shaped rods between one and six millimeters in diameter as well as sheets less than one millimeter in thickness [4]. The good processability of these alloys can be attributed to the high reduced glass temperature Trg (defined as glass transition temperature Tg divided by the liquidus temperature Tl in K) of about 0.6 to 0.63 and large supercooled liquid region ΔTx (defined as crystallization temperature minus the glass transition temperature) of at least 20° C. that are measured.